The present invention relates to a method for manufacturing a filter utilizing a porous ceramic membrane (referred to as a porous membrane hereinafter) as a separation film. In more detail, the present invention relates to a method for manufacturing a filter wherein the micro-pore size of the porous membrane can be controlled irrespective of the particle size of framework particles.
Filters utilizing ceramic porous membrane separation films are more useful for solid-liquid separation filters as compared with filters utilizing a polymer membrane as a separation film. In addition to the advantages that the micro-pore size of the porous ceramic membrane that determines filtration ability is precisely controllable, the ceramic filter is highly reliable due to its excellent physical strength, durability, and high corrosion resistance to acids or alkalis.
The filter that has been frequently used comprises a ceramic porous membrane formed on a porous substrate. Typically, the ceramic porous membrane has a far finer pore size than the porous substrate to improve filtration performance while maintaining a given water permeation rate.
The filter as described above is manufactured by a conventional slurry deposition method, for example a dipping method, wherein a slurry containing ceramic framework particles is deposited on the surface of a porous substrate, and followed by firing the deposition film.
The mean micro-pore size (simply referred to as a micro-pore size hereinafter) of the porous membrane of the filter described above is a crucial factor for determining filtration ability of the filter. The micro-pore size of the porous membrane (or the filtration ability of the filter) has previously been controlled by appropriately selecting the particle size of the framework particles in the slurry. According to the experience of the inventors of the present invention, the micro-pore size is controlled to be xc2xd to xc2xc of the particle size of the framework particles.
However, since the micro-pore size of the porous membrane described above is inevitably determined by the particle size of the framework particles, a problem arises in that the micro-pore size of the porous membrane cannot be precisely controlled when the particle size of the raw framework particles is restricted.
Accordingly, it is an object of the present invention developed in compliance with the technical problems in the conventional art to provide a method for controlling the micro-pore size of the porous membrane, irrespective of the particle size of the framework particles.
The inventors of the present invention found, through intensive studies of the technical problems in the conventional art, that the micro-pore size of the porous membrane can be controlled by adding a micro-pore size control agent comprising an organic polymer to a film deposition slurry, while appropriately changing the weight ratio between the micro-pore size control agent and the framework particles, thereby completing the present invention.
The present invention provides a method for manufacturing a filter utilizing a ceramic porous membrane as a separation film comprising the step of depositing a film deposition slurry containing ceramic framework particles on the surface of the porous membrane, wherein the slurry contains an organic polymer for expanding gaps among the framework particles, and the micro-pore size of the porous membrane is controlled by adjusting the weight ratio between the framework particles and the organic polymer in the slurry.